WPF Prism - 使用 IConfirmNavigationRequest 防止选项卡切换不起作用

Question

当使用 RequestNavigate(即以编程方式)在 View /ViewModel 之间导航时，将按预期调用适当 ViewModel 上的 IConfirmNavigationRequest 方法。但是，如果您通过单击选项卡在 TabControl 区域中切换 View ，它不会调用这些方法。

这是预期和可接受的行为吗？我能否实现 Prism 行为来完成这项工作？

如有任何建议，我们将不胜感激。

更新

我决定根据 Viktor 的反馈更彻底地解释这个问题。如果用户在屏幕上有未保存的编辑，我想阻止导航。恕我直言，切换选项卡只是另一种导航方式。我希望 Prism 实现是一致的:以编程方式或其他方式导航应该具有相同的行为。

如果我要创建一个带有按钮的 ItemsControl，当单击时使用 RequestNavigate(有效地切换选项卡)进行导航，它会起作用，但这不是问题的重点。

Answer 1

我想我明白您的意思，并且我理解您为什么希望它调用 RequestNavigate 方法。

要回答您的问题，是的，这是设计使然，不应在切换选项卡时调用 RequestNavigate。 但是，您可以修改此行为以执行您想要的操作。 Prism 是开源的。您应该拥有源代码，您可以将项目添加到您的项目中并轻松逐步执行以下代码:

TabControlRegionAdapter - 使区域适应选项卡控件

public class TabControlRegionAdapter : RegionAdapterBase<TabControl>
    {
        /// <summary>
        /// <see cref="Style"/> to set to the created <see cref="TabItem"/>.
        /// </summary>
        public static readonly DependencyProperty ItemContainerStyleProperty =
            DependencyProperty.RegisterAttached("ItemContainerStyle", typeof(Style), typeof(TabControlRegionAdapter), null);

        /// <summary>
        /// Initializes a new instance of the <see cref="TabControlRegionAdapter"/> class.
        /// </summary>
        /// <param name="regionBehaviorFactory">The factory used to create the region behaviors to attach to the created regions.</param>
        public TabControlRegionAdapter(IRegionBehaviorFactory regionBehaviorFactory)
            : base(regionBehaviorFactory)
        {
        }

        /// <summary>
        /// Gets the <see cref="ItemContainerStyleProperty"/> property value.
        /// </summary>
        /// <param name="target">Target object of the attached property.</param>
        /// <returns>Value of the <see cref="ItemContainerStyleProperty"/> property.</returns>
        public static Style GetItemContainerStyle(DependencyObject target)
        {
            if (target == null) throw new ArgumentNullException("target");
            return (Style)target.GetValue(ItemContainerStyleProperty);
        }

        /// <summary>
        /// Sets the <see cref="ItemContainerStyleProperty"/> property value.
        /// </summary>
        /// <param name="target">Target object of the attached property.</param>
        /// <param name="value">Value to be set on the <see cref="ItemContainerStyleProperty"/> property.</param>
        public static void SetItemContainerStyle(DependencyObject target, Style value)
        {
            if (target == null) throw new ArgumentNullException("target");
            target.SetValue(ItemContainerStyleProperty, value);
        }

        /// <summary>
        /// Adapts a <see cref="TabControl"/> to an <see cref="IRegion"/>.
        /// </summary>
        /// <param name="region">The new region being used.</param>
        /// <param name="regionTarget">The object to adapt.</param>
        protected override void Adapt(IRegion region, TabControl regionTarget)
        {
            if (regionTarget == null) throw new ArgumentNullException("regionTarget");
            bool itemsSourceIsSet = regionTarget.ItemsSource != null;

            if (itemsSourceIsSet)
            {
                throw new InvalidOperationException(Resources.ItemsControlHasItemsSourceException);
            }
        }

        /// <summary>
        /// Attach new behaviors.
        /// </summary>
        /// <param name="region">The region being used.</param>
        /// <param name="regionTarget">The object to adapt.</param>
        /// <remarks>
        /// This class attaches the base behaviors and also keeps the <see cref="TabControl.SelectedItem"/> 
        /// and the <see cref="IRegion.ActiveViews"/> in sync.
        /// </remarks>
        protected override void AttachBehaviors(IRegion region, TabControl regionTarget)
        {
            if (region == null) throw new ArgumentNullException("region");
            base.AttachBehaviors(region, regionTarget);
            if (!region.Behaviors.ContainsKey(TabControlRegionSyncBehavior.BehaviorKey))
            {
                region.Behaviors.Add(TabControlRegionSyncBehavior.BehaviorKey, new TabControlRegionSyncBehavior { HostControl = regionTarget });
            }
        }

        /// <summary>
        /// Creates a new instance of <see cref="Region"/>.
        /// </summary>
        /// <returns>A new instance of <see cref="Region"/>.</returns>
        protected override IRegion CreateRegion()
        {
            return new SingleActiveRegion();
        }
    }

还有 TabControlRegionSyncBehavior。 这是您可以调用 RequestNavigate 的那个。

 public class TabControlRegionSyncBehavior : RegionBehavior, IHostAwareRegionBehavior
    {
        ///<summary>
        /// The behavior key for this region sync behavior.
        ///</summary>
        public const string BehaviorKey = "TabControlRegionSyncBehavior";

        private static readonly DependencyProperty IsGeneratedProperty =
            DependencyProperty.RegisterAttached("IsGenerated", typeof(bool), typeof(TabControlRegionSyncBehavior), null);

        private TabControl hostControl;

        /// <summary>
        /// Gets or sets the <see cref="DependencyObject"/> that the <see cref="IRegion"/> is attached to.
        /// </summary>
        /// <value>A <see cref="DependencyObject"/> that the <see cref="IRegion"/> is attached to.
        /// This is usually a <see cref="FrameworkElement"/> that is part of the tree.</value>
        public DependencyObject HostControl
        {
            get
            {
                return this.hostControl;
            }

            set
            {
                TabControl newValue = value as TabControl;
                if (newValue == null)
                {
                    throw new InvalidOperationException(Resources.HostControlMustBeATabControl);
                }

                if (IsAttached)
                {
                    throw new InvalidOperationException(Resources.HostControlCannotBeSetAfterAttach);
                }

                this.hostControl = newValue;
            }
        }

        /// <summary>
        /// Override this method to perform the logic after the behavior has been attached.
        /// </summary>
        protected override void OnAttach()
        {
            if (this.hostControl == null)
            {
                throw new InvalidOperationException(Resources.HostControlCannotBeNull);
            }

            this.SynchronizeItems();

            this.hostControl.SelectionChanged += this.OnSelectionChanged;
            this.Region.ActiveViews.CollectionChanged += this.OnActiveViewsChanged;
            this.Region.Views.CollectionChanged += this.OnViewsChanged;
        }

        /// <summary>
        /// Gets the item contained in the <see cref="TabItem"/>.
        /// </summary>
        /// <param name="tabItem">The container item.</param>
        /// <returns>The item contained in the <paramref name="tabItem"/> if it was generated automatically by the behavior; otherwise <paramref name="tabItem"/>.</returns>
        protected virtual object GetContainedItem(TabItem tabItem)
        {
            if (tabItem == null) throw new ArgumentNullException("tabItem");
            if ((bool)tabItem.GetValue(IsGeneratedProperty))
            {
                return tabItem.Content;
            }

            return tabItem;
        }

        /// <summary>
        /// Override to change how TabItem's are prepared for items.
        /// </summary>
        /// <param name="item">The item to wrap in a TabItem</param>
        /// <param name="parent">The parent <see cref="DependencyObject"/></param>
        /// <returns>A tab item that wraps the supplied <paramref name="item"/></returns>
        protected virtual TabItem PrepareContainerForItem(object item, DependencyObject parent)
        {
            TabItem container = item as TabItem;
            if (container == null)
            {
                object dataContext = GetDataContext(item);
                container = new TabItem();
                container.Content = item;
                container.Style = TabControlRegionAdapter.GetItemContainerStyle(parent);
                container.DataContext = dataContext; // To run with SL 2
                container.Header = dataContext; // To run with SL 3                  
                container.SetValue(IsGeneratedProperty, true);
            }

            return container;
        }

        /// <summary>
        /// Undoes the effects of the <see cref="PrepareContainerForItem"/> method.
        /// </summary>
        /// <param name="tabItem">The container element for the item.</param>
        protected virtual void ClearContainerForItem(TabItem tabItem)
        {
            if (tabItem == null) throw new ArgumentNullException("tabItem");
            if ((bool)tabItem.GetValue(IsGeneratedProperty))
            {
                tabItem.Content = null;
            }
        }

        /// <summary>
        /// Creates or identifies the element that is used to display the given item.
        /// </summary>
        /// <param name="item">The item to get the container for.</param>
        /// <param name="itemCollection">The parent's <see cref="ItemCollection"/>.</param>
        /// <returns>The element that is used to display the given item.</returns>
        protected virtual TabItem GetContainerForItem(object item, ItemCollection itemCollection)
        {
            if (itemCollection == null) throw new ArgumentNullException("itemCollection");
            TabItem container = item as TabItem;
            if (container != null && ((bool)container.GetValue(IsGeneratedProperty)) == false)
            {
                return container;
            }

            foreach (TabItem tabItem in itemCollection)
            {
                if ((bool)tabItem.GetValue(IsGeneratedProperty))
                {
                    if (tabItem.Content == item)
                    {
                        return tabItem;
                    }
                }
            }


            return null;
        }

        /// <summary>
        /// Return the appropriate data context.  If the item is a FrameworkElement it cannot be a data context in Silverlight, so we use its data context.
        /// Otherwise, we just us the item as the data context.
        /// </summary>
        private static object GetDataContext(object item)
        {
            FrameworkElement frameworkElement = item as FrameworkElement;
            return frameworkElement == null ? item : frameworkElement.DataContext;
        }

        private void SynchronizeItems()
        {
            List<object> existingItems = new List<object>();
            if (this.hostControl.Items.Count > 0)
            {
                // Control must be empty before "Binding" to a region
                foreach (object childItem in this.hostControl.Items)
                {
                    existingItems.Add(childItem);
                }
            }

            foreach (object view in this.Region.Views)
            {
                TabItem tabItem = this.PrepareContainerForItem(view, this.hostControl);
                this.hostControl.Items.Add(tabItem);
            }

            foreach (object existingItem in existingItems)
            {
                this.Region.Add(existingItem);
            }
        }

        private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            // e.OriginalSource == null, that's why we use sender.
            if (this.hostControl == sender)
            {
                foreach (TabItem tabItem in e.RemovedItems)
                {
                    object item = this.GetContainedItem(tabItem);

                    // check if the view is in both Views and ActiveViews collections (there may be out of sync)
                    if (this.Region.Views.Contains(item) && this.Region.ActiveViews.Contains(item))
                    {
                        this.Region.Deactivate(item);
                    }
                }

                foreach (TabItem tabItem in e.AddedItems)
                {
                    object item = this.GetContainedItem(tabItem);
                    if (!this.Region.ActiveViews.Contains(item))
                    {
                        this.Region.Activate(item);
                    }
                }
            }
        }

        private void OnActiveViewsChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            if (e.Action == NotifyCollectionChangedAction.Add)
            {
                this.hostControl.SelectedItem = this.GetContainerForItem(e.NewItems[0], this.hostControl.Items);
            }
            else if (e.Action == NotifyCollectionChangedAction.Remove
                && this.hostControl.SelectedItem != null
                && e.OldItems.Contains(this.GetContainedItem((TabItem)this.hostControl.SelectedItem)))
            {
                this.hostControl.SelectedItem = null;
            }
        }

        private void OnViewsChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            if (e.Action == NotifyCollectionChangedAction.Add)
            {
                int startingIndex = e.NewStartingIndex;
                foreach (object newItem in e.NewItems)
                {
                    TabItem tabItem = this.PrepareContainerForItem(newItem, this.hostControl);
                    this.hostControl.Items.Insert(startingIndex, tabItem);
                }
            }
            else if (e.Action == NotifyCollectionChangedAction.Remove)
            {
                foreach (object oldItem in e.OldItems)
                {
                    TabItem tabItem = this.GetContainerForItem(oldItem, this.hostControl.Items);
                    this.hostControl.Items.Remove(tabItem);
                    this.ClearContainerForItem(tabItem);
                }
            }
        }
    }

当然，您必须弄清楚在哪里调用 RequestNavigate，这样您才能真正取消 TabSelectionChanging。遗憾的是，WPF 中不存在此事件。我会求助于 Josh Smith How to Prevent a TabItem from changing 推荐的技巧